Harvard Health Letter

By the way, doctor: Is the difference between the two blood pressure numbers important?

Q. I'm 72 and my systolic blood pressure has been between 115 and 125 and pretty steady. The diastolic number is low (55–65) and seems to be falling. Is the difference between these two numbers important, and is the falling diastolic number something to worry about?

A. The systolic pressure represents the blood pressure against the vessel walls when the heart is pumping blood. Starting at about age 60, it becomes the most important predictor of cardiovascular problems like stroke and heart disease. You should feel very good about your systolic blood pressure, which is in a fine range.

Diastolic pressure measures the force exerted by blood against vessel walls when the heart is relaxing between beats — that's why it's the lower of the two blood pressure numbers. With age, our arteries get a little stiff. As a result, they don't stretch out as much every time the heart beats, so more blood gets pushed right on through the larger vessels into smaller ones. Because there's less blood in the large arteries between heartbeats, diastolic pressure tends to decrease.

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